1. Flow and Physical Properties of Fractionated Ground Loblolly Pine
Oginni, O.1; Fasina, O2., Adhikari, S2. and Fulton, J3.
1School of Natural Resources, West Virginia University, Morgantown WV
2Department of Biosystems Engineering, Auburn University, Auburn AL
3College of Engineering, Ohio State University, Columbus, OH

2. BACKGROUND ON BULK MATERIALS
Conversion
Processed
Stored
Product
Gathering
Preprocessing
Storage
Further Processing

3. Flow patterns in storage equipment
Funnel flow occurs when the particles start moving out through a central ‘funnel’ that forms within the material, after which the particles against the wall collapse and move through the funnel.
Mass flow occurs when the discharge orifice is large enough to prevent the formation of cohesive arches and all the particles are in motion and move downward towards the opening.
Mass flow
Funnel flow
Source:

4. Flow problems Personnel safety risks Environmental hazards
Litigation or liability
Complete production unit shutdown
Arching/Bridging – mass flow
hammering
hammer rash
Obtaining a reliable and consistent flow out of storage equipment without flow obstruction, excessive spillage and dust generation is instrumental to successful downstream unit operations.
Have hammer rash
The hoppers of storage vessels and containers in bulk solids processing plants often appear to be afflicted with mumps or measles. But on closer inspection, it’s clear that the rash-like disease isn’t biological. Rather, it’s caused by humans who bash the hopper sides with sledge hammers, steel rods, baseball bats, or anything else that can help dislodge powder buildup inside the hopper and get it flowing again.Not only can this violence lead to armor back injuries for theworker swinging the hammer, but the noise it generates is ear-rattling.Theworst tragedy resulting from a plugged hopper, of course, is when a worker climbs inside the hopper to clean out the blockage and instead is trapped under collapsing powder, with sometimes fatal results.
vibrator
steel rod hole
jenike.com; brookfield.com
Ratholing – funnel flow
Solving flow problem?

5. Silo failure due to flow problems
Jenike.com
If the actual wall friction angle is lower than the selected design value, less vertical load will be transferred, through friction, to the cylinder walls, and the wall
pressures in the hopper will be significantly larger than was expected. Alternatively, higher wall friction results in higher compressive
loads in cylinder walls, which can cause buckling.
There are many examples of collapsing ratholes creating a vacuum and sucking in the roof and top part of a silo and/or very high pressure blowing off the hopper or causing damage to the support structure and foundation. We have had experience with loads large enough to tear a hole in a 0.5" (12.7 mm) thick stainless steel plate and enough to move a 2000 ton silo by shearing its foundation bolts.
Powderbulksolids.com
Powderandbulk.com

6. Average of 20 death per year in silo death
Source:

7. Bulk Material Flow Properties
For safe design of silos, hoppers and storage containers
Flow
Strength
Biomass is a bulk biological material

8. Main Contributors to Bulk Materials Flow Properties
Moisture content
Particle size

9. Objectives of the study
Quantify the flow properties of fractionated ground loblolly pine

10. Methodology
Loblolly wood chips were air dried and ground in a hammer mill fitted with 3.18 mm screen.
Moisture content of ground samples was adjusted to five (5) moisture content levels using the humidity chamber.
Moisture adjusted ground samples were fractionated into six (6)size classes using a sieve shaker.
Hammer mill
Humidity chamber
Sieve shaker

11. Set Moisture content % (wb) Achieved Moisture content % (wb)
After grinding (3.18 mm screen), samples were fractionated and moisture content adjusted
Screen size class (mm)
US Sieve No
0.05
pan
0.25 60
0.50 35
0.71 25
1.00 18
1.40 12
Set Moisture content % (wb)
Achieved Moisture content % (wb) 5
4.8 10
8.7 15
16.5 20
22.2 25
25.5

12. Flow and wall friction characterization
Normal load
Bracket
Cover
Shear stress
Bulk Solid
Bulk Solid
Ring
Powder Flow Tester
Unconfined Yield Strength
Flow Properties
Angle of Wall Friction
Flow Function
Major consolidating stress
Flow Index
Cohesion
Angle of Internal Friction
Flow friction test
Shear
plane
Bulk Solid
SA (1996) Loads on bulk solids containers - AS ,
Standards Australia.
Stainless steel
Mild steel
Tivar 88
Cohesion is a measure of the strength retained by a powder after it has been compacted to a given consolidation level
Angle of internal friction represents the friction between sliding layers of powder
Angle of wall friction is the frictional resistance to powder flow that exists between the powder and the wall of the container
Wall friction test
Flow and wall friction characterization

13. Bulk density apparatus Gas pycnometer
Physical properties
Hausner ratio
Particle density
Porosity
Particle size
Tap density
Compressibility
Design and selection of handling and logistic systems.
Estimation of storage vessel capacity.
Determination of feedstock quality supplied to the bio-refinery.
Design of biomass conversion equipment.
Camsizer
Bulk density apparatus
Gas pycnometer
Tap density apparatus
Energy content, ash content and volatile matter were measured using ASTM Standards
Statistical analysis was carried out on the measured properties using SAS and Microsoft Excel.

14. RESULTS

15. Similar trend were obtained for the other fractions.
Particle size distribution of fractionated ground loblolly pine at 4.78% moisture level.
Particle size distribution of fractionated ground loblolly pine at 25.53% moisture level.

16. Results
Flow function of fractionated loblolly pine at 4.78% moisture content.
Flow function of fractionated loblolly pine at 22.21% moisture content.

17. Flow classification - particle size and moisture content effects
Screen
size (mm)
Flow Index
Classification
4.78%
8.69%
16.53%
22.21%
25.53%
1.40
4.29
4.17
4.11
3.37
3.41
Easy flowing
1.00
3.80
3.49
2.73
Cohesive
0.71
3.62
2.92
2.91
2.63
2.83
0.50
3.16
2.86
2.44
2.34
2.29
0.25
2.52
2.26
2.24
2.48
0.05
2.38
2.13
2.27
2.08
NC* 
Raw
3.19
2.89
2.54
2.70
2.61
Fraction is cohesive
NC*: Experiment was not conducted at that moisture content
Jenike classification of powder flowability by flow index
Flowability
Hardened
Very cohesive
Cohesive
Easy flow
Free flowing
Flow index
<1
<2
<4
<10
>10

18. Angle of internal friction of fractionated ground loblolly pine
Screen
size (mm)
Moisture content levels (% wb)
4.78
8.69
16.53
22.21
25.53
0.05
49.88[a,x]
52.66[a,v]
51.74[a,vw]
51.55[a,w]
NC*
0.25
46.57[b,y]
48.15[b,x]
49.43[b,w]
50.89[ab,v]
50.69[a,v]
0.50
43.88[c,x]
45.29[c,x]
47.37[c,w]
49.52[bc,v]
49.49[b,v]
0.71
42.12[cd,x]
43.85[cd,w]
46.67[cd,v]
47.95[c,v]
48.09[c,v]
1.00
41.63[e,x]
42.78[d,x]
46.13[d,w]
48.23[c,v]
48.36[c,v]
1.40
40.40[e,z
42.09[d,y]
44.70[e,x]
48.15[c,v]
46.41[d,w]
Raw
43.29[cd,x]
45.51[c,w]
47.40[c,v]
48.93[c,v]
48.08[c,v]
Moisture increase increased angle of internal friction – will reduce pressure on silo wall
Size increase decreased angle of internal friction – will increase pressure on silo and hopper wall i.e. smaller sized /fine samples will increase pressure on silo wall – material disintegrate during storage and turn into fines.
At high moisture content, size effect small
Particle size effect: values in each column with same letter (a-f) are not significantly different (p<0.05).
Moisture effect: values in each row with same letter (v-z) are not significantly different (p<0.05).
NC* experiment was not conducted because there was no fraction at 25.53% moisture level.

19. Angle of internal friction of fractionated ground loblolly pine
Screen
size (mm)
Moisture content levels (% wb)
4.78
8.69
16.53
22.21
25.53
0.05
49.88[a,x]
52.66[a,v]
51.74[a,vw]
51.55[a,w]
NC*
0.25
46.57[b,y]
48.15[b,x]
49.43[b,w]
50.89[ab,v]
50.69[a,v]
0.50
43.88[c,x]
45.29[c,x]
47.37[c,w]
49.52[bc,v]
49.49[b,v]
0.71
42.12[cd,x]
43.85[cd,w]
46.67[cd,v]
47.95[c,v]
48.09[c,v]
1.00
41.63[e,x]
42.78[d,x]
46.13[d,w]
48.23[c,v]
48.36[c,v]
1.40
40.40[e,z
42.09[d,y]
44.70[e,x]
48.15[c,v]
46.41[d,w]
Raw
43.29[cd,x]
45.51[c,w]
47.40[c,v]
48.93[c,v]
48.08[c,v]
Moisture increase increased angle of internal friction – will reduce pressure on silo wall
Size increase decreased angle of internal friction – will increase pressure on silo and hopper wall i.e. smaller sized /fine samples will increase pressure on silo wall – material disintegrate during storage and turn into fines.
At high moisture content, size effect small
Particle size effect: values in each column with same letter (a-f) are not significantly different (p<0.05).
Moisture effect: values in each row with same letter (v-z) are not significantly different (p<0.05).
NC* experiment was not conducted because there was no fraction at 25.53% moisture level.

20. Angle of wall friction of fractionated loblolly pine on mild steel
Screen
size (mm)
Moisture Content Level (% wb)
4.78
8.69
16.53
22.21
25.53
0.05
12.33[a,x]
16.10[a,w]
15.22[a,w]
21.35[a,v]
NC*
0.25
10.48[d,z]
13.11[b,y]
14.29[c,x]
18.12[bc,w]
22.56[a,v]
0.50
10.50[cd,z]
12.09[c,y]
15.07[a,x]
18.18[bc,w]
19.52[b,v]
0.71
10.54[cd,z]
12.17[c,y]
15.31[a,x]
17.42[c,w]
19.73[b,v]
1.00
10.81[b,z]
12.43[c,y]
15.01[ab,x]
17.99[c,w]
18.87[bc,v]
1.40
10.76[bc,y]
12.38[c,x]
14.22[c,w]
18.00[c,v]
18.30[c,v]
Raw
10.55[bc,y]
12.16[c,x]
14.53[bc,w]
19.04[b,v]
19.39[bc,v]
Moisture content increase increased angle of wall fiction
Angle of wall friction increased with decrease in particle size
Since pressure reduces with increase in angle of wall friction, then smaller particles reduces wall pressure
– effect very small but slight reduction in wall pressure
Angle of wall
Particle size effect: values in each column with same letter (a-f) are not significantly different (p<0.05).
Moisture effect: values in each row with same letter (w-z) are not significantly different (p<0.05).
NC* experiment was not conducted because there was no fraction at 25.53% moisture level.

21. Angle of wall friction of fractionated loblolly pine on mild steel
Screen
size (mm)
Moisture Content Level (% wb)
4.78
8.69
16.53
22.21
25.53
0.05
12.33[a,x]
16.10[a,w]
15.22[a,w]
21.35[a,v]
NC*
0.25
10.48[d,z]
13.11[b,y]
14.29[c,x]
18.12[bc,w]
22.56[a,v]
0.50
10.50[cd,z]
12.09[c,y]
15.07[a,x]
18.18[bc,w]
19.52[b,v]
0.71
10.54[cd,z]
12.17[c,y]
15.31[a,x]
17.42[c,w]
19.73[b,v]
1.00
10.81[b,z]
12.43[c,y]
15.01[ab,x]
17.99[c,w]
18.87[bc,v]
1.40
10.76[bc,y]
12.38[c,x]
14.22[c,w]
18.00[c,v]
18.30[c,v]
Raw
10.55[bc,y]
12.16[c,x]
14.53[bc,w]
19.04[b,v]
19.39[bc,v]
Moisture content increase increased angle of wall fiction
Angle of wall friction increased with decrease in particle size
Since pressure reduces with increase in angle of wall friction, then smaller particles reduces wall pressure
– effect very small but slight reduction in wall pressure
Angle of wall
Particle size effect: values in each column with same letter (a-f) are not significantly different (p<0.05).
Moisture effect: values in each row with same letter (w-z) are not significantly different (p<0.05).
NC* experiment was not conducted because there was no fraction at 25.53% moisture level.

22. Moisture Content Level (% wb)
Angle of wall friction of fractionated loblolly pine on Tivar 88 surface
Screen size (mm)
Moisture Content Level (% wb)
4.78
8.69
16.53
22.21
25.53
0.05
14.80[a,vw]
15.54[a,v]
14.52[a,w]
15.50[a,v]
NC*
0.25
13.61[b,w]
13.48[bc,w]
13.14[b,w]
13.33[c,w]
15.23[a,v]
0.50
12.48[c,w]
12.87[cd,vw] ±
12.83[b,vw]
12.36[d,w]
13.06[b,v]
0.71
12.10[cd,v]
12.32[de,v]
12.01[c,v]
12.02[d,v]
11.76[c,v]
1.00
11.59[d,w]
11.72[ef,w]
11.24[d,w]
12.81[cd,v]
11.46[c,w]
1.40
10.88[e,y]
11.47[f,vw]
11.61[cd,w]
12.44[cd,v]
10.98[c,xy]
Raw
11.75[d,x]
14.07[b,v]
12.17[c,wx]
14.45[b,v]
12.55[b,w]
Particle size effect: values in each column with same letter (a-f) are not significantly different (p<0.05).
Moisture effect: values in each row with same letter (v-z) are not significantly different (p<0.05).
NC* experiment was not conducted because there was no fraction at 25.53% moisture level.

23. Sensitivity of hopper angle to physical and flow properties
From structural design; want high moisture and small particle size because both conditions result in low bulk density and high angle of internal friction
From functional design, want larger particle size and low moisture content.
0.05 mm fraction
1.40 mm fraction
d = angle of internal friction; fw = angle of wall friction; a = hopper half angle

24. Scanning Electronic Microscope Images of the Wall Materials
Stainless steel
Mild steel
Ultra- high weight molecular polyethylene (Tivar 88)
(Sources: Zhou and Komvopoulos, 2005; Günen, et al., 2014; Farhat and Quraishi, 2010)

25. Ash contents of fractionated ground loblolly pine

26. Energy and volatile matter contents of fractionated ground loblolly pine

27. Bulk density of fractionated ground loblolly pine.
Bulk density significantly increased with increase in fraction size and with decrease in moisture content. Increased cohesion = low bulk density
Increase in bulk density will increase pressure on wall of silo.
Seems that fraction size has more effect on silo for bulk density and angle of internal friction. Decrease in angle of internal friction and increase in bulk density increases pressure on wall. However, bulk density increased with increase in fraction size, while angle of internal friction reduced with increased in fraction size. The overall effect is that pressure on silo wall is highest for small fines.
The tap density significantly increased with increase in fraction size and reduction in moisture content. Increase in volume higher than increase in mass due to moisture.
Bulk density of fractionated ground loblolly pine.
Particle density of fractionated ground loblolly pine.

28. Bulk density of fractionated ground loblolly pine.
Bulk density significantly increased with increase in fraction size and with decrease in moisture content. Increased cohesion = low bulk density
Increase in bulk density will increase pressure on wall of silo.
Seems that fraction size has more effect on silo for bulk density and angle of internal friction. Decrease in angle of internal friction and increase in bulk density increases pressure on wall. However, bulk density increased with increase in fraction size, while angle of internal friction reduced with increased in fraction size. The overall effect is that pressure on silo wall is highest for small fines.
The tap density significantly increased with increase in fraction size and reduction in moisture content. Increase in volume higher than increase in mass due to moisture.
Bulk density of fractionated ground loblolly pine.
Particle density of fractionated ground loblolly pine.

29. Porosity of fractionated ground loblolly pine.

30. Conclusion
Flow and physical properties of ground loblolly pine are significantly affected by particle size and moisture content
Hopper half angle decreased (from 15o to 38o) with particle size and with increase in moisture content
Use of lining material (e.g. TIVAR) on hopper wall will minimize the effects of particle size and moisture content on hopper design

31. Acknowledgment

32. THANK YOU FOR YOUR TIME.

33. Moisture content % (wb)
Dosing Experiment
Mixture of 1.40mm and 0.50 mm fractions at a ratio of 10:1, 10:2 and 10:3 in order to determine the point at which the 1.40mm fraction turns from ‘easy flowing to cohesive’.
Moisture content % (wb)
Ratio
10:1
10:2
10:3
4.78
3.92
3.75
3.45
8.69
4.00
3.90
3.41
16.53
3.70
3.23

34. Hausner ratio of fractionated ground loblolly pine.
Flowability classification using Hausner ratio (Source: Carr, 1965).
Hausner ratio
Flow character
Excellent
Good
Fair
Passable
Poor
Very poor
>1.60
Very, very poor
Ratio of tap density to bulk density.
Hausner ratio of fractionated ground loblolly pine.

35. Compressibility of fractionated ground loblolly pine.
Flowability classification of bulk solids (Fayed and Skocir, 1997).
Compressibility (%)
Flow
5 - 15
excellent flow
good flow
fair to passable flow
poor flow
very poor flow
> 40
extremely poor flow
Compressibility of fractionated ground loblolly pine.

36. Tap density of fractionated ground loblolly pine.